This invention relates to electronic devices, and particularly, but not limited, to semiconductor devices of the type including a plurality of elongated leads bonded in side-by-side relation to conductive paths on a substrate.
One type of known semiconductor device comprises a substrate, e.g., of ceramic, having a fan-like (diverging) pattern of conductive paths on a surface thereof, and a semiconductor chip mounted face down on the substrate. Different conductive paths on the chip are electrically connected to different ones of the substrate paths at the area of convergence thereof. The diverging substrate paths terminate at bonding pads, generally disposed along edges of the substrate, and elongated metal conductive members or leads are bonded to the bonding pads to provide electrical terminals for the completed device.
In the assembly of such devices, it is the practice to provide the device leads as part of a unitary assembly or frame. The leads are arrayed in a pattern corresponding to that of the substrate bonding pads whereby all the leads can be simultaneously aligned and simultaneously bonded to the bonding pads. The leading interconnecting portions of the lead frame are then removed leaving the leads bonded to and extending away from the substrate.
For purposes of miniaturization, it is desirable to space the bonding pads as closely together as possible on the substrates. One problem caused by such close spacing is that relatively slight misalignment of the lead frames with the substrates can cause shorting together of adjacent bonding pads by misaligned leads which are disposed between and in overlapped relation with adjacent pads rather than in contact with single ones only of the pads.
One solution to this problem is to simply increase the size of the substrates and the bonding pad spacings. This, of course, is contrary to achieving maximum miniaturization. Another solution is the use of more complex and accurate lead frame alignment apparatus. This involves greater capital expense. A third solution is to reduce the width of the bonding pads or the leads, or both, thus reducing the likelihood of adjacent pads being spanned and shorted together by the leads. A limit to how far this solution could heretofore be extended, however, is that below a minimum area of contact between the leads and the bonding pads, such contact area being a function of the width of the leads and pads, the strength of adhesion of the leads to the substrate is inadequately small.
One object of this invention is to provide an arrangement wherein, without significantly reducing the strength of the bonds between the leads and the substrates, or increasing the size of the devices, the likelihood of shorting together adjacent bonding pads by misaligned leads is reduced.